Help with RAM purchase

Hi, getting ready to buy new memory 2 2gb modules, it says that my board can run at 1066Mhz but I dont think my memory will load that. What would be good compatible ram for my system to get 1066Mhz,
MOBO M2n68-AM PLUS
CPU AMD Athlon 64x2 factory 1.9ghz OC 2.5Ghzx2
4 Gb RAM 400Mhz
Graphics Card Nvidia Geforce 8400 GS OC 800Mhz GPU
500GB SATA HDD
OKIA 450 Watt power supply
Is there any way to override the 400mhz that my ram says is the max frequency?
Any help would be great

Your memory now run at 800Mhz. Because is running in dual channel you see 400 , in fact is running 400x2 = 800 because you have two memory sticks .To run at 1066 you need memory that run native 1066Mhz. In your motherboard will run at 800Mhz ( 400x2 ) and just with overclock will run at 1066Mhz.